Fesoterodine, namely (R)-2-(3-diisopropylamino-1-phenylpropyl)-4-(hydroxymethyl)-phenol isobutyrate, of formula (I)

is a known compound with antimuscarinic activity, clinically used as the fumarate, for the treatment of the hyperactive bladder syndrome and particularly of urinary incontinence.
U.S. Pat. No. 6,713,464 discloses the preparation of Fesoterodine through different synthetic methods, as reported e.g. in the Scheme hereinbelow.

One of these methods makes use of a racemic key intermediate of formula (A)

obtainable in three steps from 4-bromophenol. After resolution, through formation of the diastereomeric salts, the methylpropionic side chain of the optically active compound of formula (Ab) is transformed into the diisopropylamine side chain of the compound of formula (B).
Compound (C) is obtained, through C-1 homologation of the Grignard reagent of compound of formula (B) with solid CO2, to afford compound (D), that is subsequently reduced with LiAlH4. This step was optimized in WO 2007/144091, as reported in the above Scheme, by directly reacting the Grignard reagent of compound (B) with paraformaldehyde or trioxane. Compound (C) is then converted to Fesoterodine upon debenzylation and selective esterification of the resulting phenol compound.
As it can be noted, these processes are quite long lasting and complex, and require protective groups for the phenol hydroxyl group, thus involving an increase in number of steps and negatively affecting both yields and industrialization of the process.
There is therefore the need for an alternative synthesis which provides Fesoterodine or a salt thereof with high purity, from low cost starting materials and with an efficient process that can be reproduced on an industrial scale.